Nonvolatile memories using resistance materials include phase-change random access memories (PRAMs), resistive RAMs (RRAMs), and magnetic RAMs (MRAMs). While dynamic RAMs (DRAMs) or flash memories store data using charges, nonvolatile memories using resistance materials store data using a state change of a phase-change material, such as chalcogenide alloy (in the case of PRAMs), a resistance change of a variable resistance material (in the case of RRAMs), or a resistance change of a magnetic tunnel junction (MTJ) thin film according to a magnetization state of a ferromagnetic material (in the case of MRAMs).
For example, in a phase-change memory device, a phase-change material is changed into a crystalline state or an amorphous state while being heated and then cooled. The phase-change material typically exhibits a relatively low resistance in the crystalline state, which is typically defined as “set” data, and a relatively high resistance in the amorphous state, which is typically defined as “reset” data.